In the course of our ongoing multiplicity study of exoplanet host stars we detected a faint companion located at ∼43 arcsec (480 au physical projected separation) north-west of its primary – the exoplanet host star HD 3651 at 11 pc. The companion, HD 3651 B, clearly shares the proper motion of the exoplanet host star in our four images, obtained with the European Southern Observatory New Technology Telescope and the United Kingdom Infrared Telescope, spanning three years in epoch difference. The magnitude of the companion is H= 16.75 ± 0.16 mag, the faintest co-moving companion of an exoplanet host star imaged directly. HD 3651 B is not detected in the POSS-II B-, R- or I-band images, indicating that this object is fainter than ∼20 mag in the B- and R-band and fainter than ∼19 mag in the I-band. With the Hipparcos distance of HD 3651 of 11 pc, the absolute magnitude of HD 3651 B is about 16.5 mag in the H band. Our H-band photometry and the Baraffe et al. (2003) evolutionary models yield a mass of HD 3651 B to be 20 to 60 MJup (Jupiter masses) for assumed ages between 1 and 10 Gyr. The effective temperature ranges between 800 and 900 K, consistent with a spectral type of T7 to T8. We conclude that HD 3651 B is a brown dwarf companion, the first of its kind directly imaged as a companion of an exoplanet host star, and one of the faintest T dwarfs found in the solar vicinity (within 11 pc).

The first results of a new survey, which explores the second data release of the ESA‐Gaia mission, are reported in order to search for stellar companions of (Community) TESS Objects of Interest and to characterize their properties. In total, 193 binary and 15 hierarchical triple star systems are presented, detected among 1,391 target stars, which are located at distances closer than about 500 pc around the Sun. The companions and the targets are equidistant and share a common proper motion, as is expected for gravitationally bound stellar systems, proven with their accurate Gaia astrometry. The companions exhibit masses in the range between about 0.08 M_⊙ and 3M_⊙ and are most frequently found in the mass range between 0.13 and 0.6M_⊙. The companions are separated from the targets by about 40 up to 9,900 au, and their frequency continually decreases with increasing separation. While most of the detected companions are late K to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature is revealed by their photometric properties.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We present the latest results of our ongoing multiplicity study of (Community) TESS Objects of Interest, using astro‐ and photometric data from the ESA‐Gaia mission, to detect stellar companions of these stars and to characterize their properties. In total, 107 binary, 5 hierarchical triple star systems, as well as one quadruple system were detected among 585 targets surveyed, which are all located at distances closer than about 500 pc around the Sun. As proven with their accurate Gaia EDR3 astrometry, the companions and the targets are located at the same distance and share a common proper motion, as it is expected for components of gravitationally bound stellar systems. The companions exhibit masses in the range between about 0.09 M_⊙ and 4.5 M_⊙ and are most frequently found in the mass range between 0.15 and 0.6 M_⊙. The companions are separated from the targets by about 120 up to 9,500 au and their frequency is the highest and constant within about 500 au while it continually decreases for larger separations. Beside mainly early to mid M dwarfs, also five white dwarf companions were identified in this survey, whose true nature was revealed by their photometric properties.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics